1. Field of the Invention
The invention relates to a method for measuring a rotary tool, rotatable about a rotation axis and mounted in a tool mounting having a tool contour determining the working dimensions of the rotary tool using a measuring device, which has an optical image acquisition device with an optics orientable onto the rotary tool for acquiring images of said rotary tool and an image processing device connected to the image acquisition device for the computer-aided evaluation of the acquired images, as well as a measuring device suitable for performing the method.
2. Description of the Prior Art
Rotary tools are e.g. used in working machines for the material-removing and in particular cutting working of workpieces. For example for the manufacture of precise holes or bores use is made of cutting devices in which the working or active dimensions of the tool are determined by a replaceable and adjustable tool cutting edge. In order to be able to respect the presently required, very close manufacturing tolerances and demands concerning the surface quality, bore shape, etc., such rotary tools must be measured in micrometer-precise manner and optionally precisely set for the particular application. Apart from the requirement of high precision measurement, with respect to optimized production sequences there is also a need for high speed of the tool measurement and setting.
In order in the case of manual tool setting to be able to fulfill the contradictory requirements of speed and precision, nowadays in place of the previously conventional tool measuring and setting devices with projectors, increasing use is being made of measuring devices, which comprise an optoelectronic image acquisition device and an image processing device connected thereto for computer-aided evaluation of acquired images. The image acquisition device normally has a CCD video camera, whose optics are aligned with the tool to be measured or on the area of the tool contour to be measured. The arrangement between the optics and the tool is to be so set during measurement that the rotation axis of the rotary tool is oriented perpendicular to the optical axis of the optics and passes through the area of the sharpness or definition zone of the optics. The camera is normally placed on a slide or carriage, which is movable in two directions perpendicular to the optical axis. Conventionally a direction running parallel to the tool mounting axis is called the Z-direction and a radial direction perpendicular thereto the X-direction. In the case of rotary tools, whose rotation axis in the case of a correct setting coincides with the tool mounting rotation axis, the Z-direction corresponds to the tool longitudinal direction, so that a Z-value corresponds to a tool length and a X-value to a tool radius.
A conventional, image processing-aided measuring sequence commences with an operator moving the tool contour to be measured (tool cutting edge) roughly into the image field of the optics with the aid of the X-Z-slide. The tool cutting edge then becomes visible in a monitor connected to the image acquisition device. In the following step the tool cutting edge to be measured is focussed in that the operator rotates the rotary tool about its rotation axis until the tool contour to be measured is located in the sharpness zone of the optics and is consequently focussed. The focussing step critical for the precision of the measurement is facilitated in certain known devices with image processing by a focussing display visible on the monitor. The focussing display is e.g. in the form of an analog bar display with colour change between red (still unsharp) and green (sharpness position) and guides the operator during focussing. Within the computer the deflection of the cutting edge contour in the radial direction (X-direction) is detected and evaluated for the focussing display. This is generally at a maximum when the tool cutting edge is in the sharpness zone. In practice the operator initially rotates the tool beyond the sharpness position and then slowly back for the actual measurement into the position of maximum sharpness corresponding to the maximum deflection in the X-direction. This focussing process is facilitated by the focussing display, which guides the operator during the focussing of the cutting edge and ensures an operator-independent focussing.
The object of the invention is to make available a tool measurement and setting aided by image processing and which permits a precise and at the same time very rapid tool measurement.
For solving this problem the invention proposes a method for measuring a rotary tool using a measuring device, the rotary tool being rotatable about a rotation axis and being mounted in a tool mounting with, the rotary tool comprising a tool contour determining the working dimensions of the rotary tool;
the measuring device comprising an optoelectronic image acquisition device including optics alignable with the rotary tool for acquiring images of the rotary tool, further comprising an image processing device connected to the image acquisition device for the computer-aided evaluation of acquired images, the method involving the following steps:
placing the area of the tool contour to be measured in an image area of the optics of the optoelectronics image acquisition device;
rotating the rotary tool about the rotation axis;
acquiring a sequence of frames of the rotating rotary tool;
computer-aided evaluation of the frames with respect to at least one image parameter, the image parameter representing a measure for the positioning of the tool contour with respect to a sharpness zone of the optics;
determining a selection frame by computer-aided selection of a frame from the sequence of frames, in which frame the image parameter corresponds to a positioning of the tool contour in the sharpness zone of the optics;
evaluation of the selection frame for determining at least one tool parameter characterizing the tool contour.
The object is also achieved by a measuring device for measuring a rotary tool, the rotary tool being rotatable about a rotation axis and being mounted in a tool mounting, the rotary tool comprising a tool contour determining the working dimensions of the rotary tool; the measuring device comprising:
an optoelectronic image acquisition device with optics alignable with the rotary tool for acquiring images of the rotary tool and;
an image processing device connected to the image acquisition device for the computer-aided evaluation of images acquired by the image acquistion device;
the image processing device comprising a frame grabber for acquiring a sequence of frames of the rotary tool and a computing unit with a working program for computeraided evaluation of the frames, wherein the working program comprises the following steps:
evaluation of the frames with respect to at least one image parameter, the image parameter representing a measure for the positioning of the tool contour with respect to the sharpness zone of the optics;
determination a selection frame by selecting a frame from the sequence of frames, in which frame the image parameter corresponds to a positioning of the tool contour in the sharpness zone of the optics;
evaluation the selection frame for determining at least one tool parameter characterizing the tool contour.
Preferred further developments are given in the dependent claims. The wording of all the claims is hereby made by reference into part of the description.
In the method according to the invention firstly a section of the rotary tool containing the tool contour to be measured is placed in the image field of the optics, which can be brought about by a suitable relative movement between optics and rotary tool. The rotary tool is rotated about its rotation axis and rotation normally only begins when the section to be measured is in the image field of the optics, but optionally also beforehand. During rotation there is an acquisition of a sequence of frames of the rotating rotary tool. These frames contain a view of the image field acquired by the optics and which corresponds to the particular acquisition time, i.e. a type of projection of the tool in a rotary position corresponding to the acquisition time. An acquisition of the rotary tool rotation position associated with a frame is unnecessary, but can take place. For frame acquisition it is possible for the image processing device to have a so-called frame grabber. There is a computer-aided evaluation of the frames and during evaluation an evaluation takes place of at least one image parameter characteristic of the tool contour and which represents a measure for the positioning of the tool contour with respect to the sharpness zone of the optics. This image parameter contains information as to whether the tool cutting edge during the acquisition of the frame was in or e.g. above or below the sharpness zone of the optics. By means of said image parameter it is possible to select from a plurality of frames a single frame which, compared with the other frames of the sequence, contains the sharpest imaging of the tool contour to be measured. This frame is referred to as the selection frame. As a function of the relationship between the rotation speed of the rotary tool and the time interval between directly following frames, there can also be several more or less equivalent frames with respect to the sharpness position and from which then at least one is selected. Thus, there is a determination of a selection frame by computer-aided selection of a frame from the sequence in which the image parameter corresponds to a positioning of the tool contour in the sharpness zone of the optics. Through the determination of the selection frame an image can so-to-speak be xe2x80x9cfrozenxe2x80x9d and this can correspond to the image which would be seen by an operator in conventional equipment after a more or less complicated focussing. Finally there is an evaluation of the selection frame for determining at least one tool parameter characterizing the tool contour, e.g. the tool radius (X-value) in the range of interest and/or the tool length (Z-value).
The advantages of the invention are in particular that there is no need for a focussing of the tool cutting edge in the conventional sense. The invention makes use of the fact that with an image acquisition and processing of frames which is sufficiently fast compared with tool rotation, at least one of the frames has acquired the tool contour of interest (tool cutting edge) in the sharpest state and said frame carries all the information which is to be determined by image acquisition and evaluation in the measuring process. As there is no need for a focussing process, the invention permits a much faster measurement with a precision of measurement at least as good as in the prior art. There is also no need for focussing display devices, i.e. for guiding the operator during focussing. The at least one determined tool parameter can be outputted and e.g. displayed on a data display means such as a monitor and/or can be stored for further processing in a storage means of the image processing device. Determinable tool parameters, apart from the indicated X and Z-quantities, include e.g. values for the cutting edge radii and angles, as well as programming quantities, such as the theoretical radius or theoretical length. In a preferred method said evaluation and optionally data output take place during tool rotation, so that a real time measurement is possible.
The situation can in particular be such that the rotation of the rotary tool takes place continuously, preferably without stopping or deceleration at the sharpness position and/or without rotating back the tool mounting in such a way that the tool cutting edge after passing through the sharpness plane is returned thereto for measurement. Thus, there is no need for the possibly repeated approach and removal with respect to the so-called radial reversal point of the tool cutting edge encountered in conventional measurements.
In a preferred embodiment the acquisition of directly succeeding frames in the sequence takes place with a time interval of less than 0.1 second and the time interval is in particular between approximately 0.01 and approximately 0.5 seconds and is preferably approximately 0.02 seconds. This virtually permits a real time measurement and it is ensured that with standard tool rotation speeds during the measurement at least one of the frames reproduces in sharply imaged form the tool contour within the resolution of the optics. It would be possible to provide separate devices for ensuring this. For example a warning indication or display can be provided, which optically and/or acoustically warns the operator as a function of the actual tool rotation speed when a maximum permitted speed limit for a precise measurement is exceeded. Alternatively or additionally it is possible to provide a limiting device, which limits the speed of the rotary tool during the measurement to a corresponding maximum speed.
A high frame frequency of e.g. 50 Hz also makes it possible to evaluate the selection frame and/or an optionally provided outputting of data in time-near manner for a preferably uninterrupted passage of the tool contour to be measured through the sharpness zone. For a micrometeraccurate measurement of interesting tool parameters, it is merely necessary to rotate the tool beyond the sharpness point. The determined values are frozen and can be immediately displayed.
The rotary movement can be repeated a random number of times by an operator or an automatic mechanism either by rotating backwards and forwards or by a multiple rotation of the tool in one direction, in order to acquire confidence in the measurement and/or determine independent measurement statistics. In the method according to the invention the desired measured values or data are redetermined during each passage of the tool contour through the sharpness zone and preferably independently of the rotation direction.
In a preferred method the image parameter by means of which there is a selection of the selection frame to be further processed, use is made of a radial spacing value X of the tool contour with respect to the rotation axis of the rotary tool. Thus, the basis for the frame selection is a simple length or spacing determination, which can be particularly rapidly performed by computer. Additionally or alternatively it is possible to use the contrast in the area of the tool contour to be measured or corresponding operands as a basis for frame selection.
According to a further development, for determining the selection frame there is a comparison of image parameters from frames acquired in different rotary positions of the rotary tool leading to an extreme value determination. The situation can e.g. be such that successive frames are successively stored in an image memory, which preferably is in the form of a buffer memory operating according to the first-in-first-out principle with several adequately dimensioned storage locations for receiving the image data of a frame. This permits a rapid image processing, in which a completely read in frame is already evaluated during the reading in in time-parallel manner of the following frame. During evaluation a contour tracking of the acquired tool contour can take place, in order to determine for the tool contour at least the extreme value of the selected reference image parameter, particularly the maximum radial deflection X and optionally also further parameters, e.g. the associated maximum length value Z. By means of a comparison routine the frame having the sought extreme image parameter value can be determined and used as a basis for further calculations. This method variant with a FIFO buffer store requires a particularly small storage location.
As stated, a measuring device suitable for performing the method has an optoelectronic image acquisition device and an image processing device connected thereto. The latter has a frame grabber for the acquisition of a sequence of frames of the rotating rotary tool and a computing unit in which is processed or operates a working program for computer-aided evaluation of the frames. The working program is constructed for performing the following steps:
evaluation of the frames with respect to at least one image parameter characteristic of the tool contour and which represents a measure for the positioning of the tool contour relative to the sharpness zone of the optics;
determination of a selection frame by selecting at least one frame in the sequence in which the image parameter corresponds to a positioning of the tool contour in the sharpness zone of the optics;
evaluation of the selected selection frame for determining at least one tool parameter characteristic of the tool contour.
Preferably, with the measuring device is associated an image display means connected to the image acquisition device and/or to the image processing device for the optical display of images acquired by the optics. The image display means preferably comprises at least one monitor. Appropriately there is also an output device for the preferably optical outputting of the tool parameters determined, which e.g. outputs to a memory and/or can be directly displayed in a data display area of the monitor.
A measuring device according to the invention can be operated in conjunction with a suitable means, which has a suitable, preferably rotary tool mounting, which is appropriately movable in at least the two axes described perpendicular to the optical axis of the optics. Thus, the measuring device can be used in conjunction with most presently available tool setting and measuring means, particularly also those relatively simply constructed means in which the rotation of the spindle having the tool mounting takes place manually.
The measuring method and the corresponding measuring device can also be used for other, corresponding measurements. A measuring device could also be directly used on a machine tool for setting or checking tools with respect to dimensions and/or concentricity, as well as for the correct positioning of the tool in a machine spindle. The invention can also be used with tools having a plurality of cutting edges and then for some or all the tool cutting edges a measurement can be performed in the above-described manner. It is also possible to measure rotary tools constructed in the manner of angle scanning heads. In the case of the latter at least one rotary tool is placed in rotary manner on a support member insertable in a tool mounting and the rotation axis of the rotary tools drivable by means of a separate drive is at an angle to the rotation axis of the tool mounting or support member.
These and further features can be gathered from the claims, description and drawings and the individual features, both singly and in the form of subcombinations, can be implemented in an embodiment of the invention and in other fields and can represent advantageous, independently protectable constructions.